During the high-pressure treatment, the products, in a high-pressure chamber, and acted on by a high-pressure medium, are treated at a pressure of up to 10 000 bar. The high-pressure medium exits the high-pressure chamber, normally in a manner controlled by means of one or more high-pressure valves, into a collecting tank where the high-pressure medium is collected as the pressure in the high-pressure chamber is reduced.
In some cases, the pressure is initially rapidly reduced to approximately 500 bar, with the pressure subsequently being expanded slowly to ambient pressure. This is also referred to as rapid and soft expansion. The pressure reduction is effected by means of various pressure valves between the high-pressure chamber and the collecting tank.
During the rapid and soft expansion, the demands on the pressure valves differ owing to different pressures and expansion gradients.
The dissipation of very high pressure differences during the rapid expansion often leads to very intense flow dynamics, associated with all possible flow erosion processes such as for example cavitation and wall friction and wet vapour erosion, which damage the valve spindle (5) and the valve seat (4). It is therefore sought to find a solution to such a problem.
The reduction of the pressure in a high-pressure chamber by means of two valves is disclosed in WO 2006/129180 A1. There, for the discharge of the high-pressure medium from the high-pressure chamber, a line with two pressure valves connected in series is provided. Between the two pressure valves there is an intermediate pressure chamber for receiving the high-pressure medium, in order for the pressure to be reduced in stepped fashion from the first pressure valve to the second pressure valve and erosion at the pressure valve to be prevented. A disadvantage is however that the cycle times of this method are very long. Furthermore, the execution of the method with the pressure valves is complex.
Document DE 10 2009 042 088 A1 describes a device and a method for the high-pressure treatment of packaged foodstuffs, wherein the pressure dissipation in a high-pressure chamber is performed in three phases. A range of different pressure valves is provided for implementing the method.
Document U.S. Pat. No. 3,010,695 discloses a high-pressure regulation valve in which the regulation characteristic can be predefined by means of a perforated ring through which flow can pass and which has orifices that can be formed differently. During operation, the regulation is performed by way of different valve spindle positions, wherein the valve spindle opens up the orifice areas to a greater or lesser extent. Low-erosion throttling of the flow in the annular gap between the perforated ring and the valve spindle is not proposed, and is also not possible in the case of the geometric proportions shown.
Document DE 10 2009032850 A1 describes a pressure-limiting valve in which the opening force effected by the medium abruptly increases; this is attained inter alia by way of an abrupt increase of the effective throughflow cross section downstream of the sealing surface of the valve seat. The problem of erosion caused by the highly dynamic flow thus generated is not discussed in the patent.
A separate construction of the high-pressure valve is disclosed in DE 44 38 462 C1, which concerns a bolt-needle valve with “soft tip” which is intended for fluid systems up to approximately 1400 bar. The high-pressure valve has a stuffing box with an auxiliary pressure chamber arranged therein, a body with an inlet and an outlet, and a seat between the inlet and the outlet. A piston is arranged in the auxiliary pressure chamber. The shank has a lateral support with a soft shank tip and has a concentric through-bore for connecting the fluid pressure from the inlet to the top side of the piston, whereby the piston moves the shank and the soft valve tip in the direction of the valve seat, and thus the actuation forces can be reduced and varied. The problem of erosion owing to highly dynamic flows is not discussed in said patent.
Owing to the high overall pressures and also the pressure differences, it is only possible for valve spindles and seats composed of high-strength materials to be used in the working range of up to 10 000 bar intended here.
To address the present problem, one would automatically attempt to use a harder material for the valve spindle and valve seat. This duly leads to an improved result in relation to the valve spindle and valve seat with relatively soft materials. However, owing to the erosion loading exerted on the valve spindle and valve seats during every expansion cycle by the high-pressure medium as it flows through, frequent exchange of the components remains unavoidable.
Avoidance of the critical highly dynamic flow states can be achieved by means of flow resistances positioned upstream and/or downstream, wherein the expansion rate is however greatly reduced. This is however undesirable in the case of time-critical applications.
In the construction of a high-pressure valve, it is necessary in particular for the valve spindle and valve seat to be coordinated with one another with regard to the material pairings used and also with regard to the design of the components.